Copyright (c) 1991 Edward de Bono

This game is played on a 4x4 square board:

  • TURNS - On each turn, each player must pick his friendly L, make any series of turns and flips, and drop it on an empty position (it is invalid to place in at the previous position).
    • Then the player may optionally move one neutral stone (the red stones in the diagram) to any empty cell.
  • GOAL - Wins the player that stalemates the adversary.

An example

Black's turn.

Black flips his L and drops it on another empty position. He also moves the neutral stone at a1 to b4. Now White cannot move and loses the game.

From In a game with two perfect players, neither will ever win or lose, unless one thinks of something better to do, and loses on purpose. One basic strategy is to use a neutral piece and one's own piece to block a 3x3 square in one corner, and use a neutral piece to prevent the opponent's L piece from swapping to a mirror-image position.
[...] One of the problems with the game is that defensive play can continue indefinitely if the players are too cautious [...]. If both players are at this level, a sudden-death variant of the rules permits one to move both neutral pieces after moving.